Artificial heart valves desirably last at least ten years in vivo. To last that long, artificial heart valves should exhibit sufficient durability for at least four hundred million cycles or more. The valves, and more specifically heart valve leaflets, must resist structural degradation including the formation of holes, tears, and the like as well as adverse biological consequences such as calcification and thrombosis.
Fluoropolymers, such as expanded and non-expanded forms of polytetrafluoroethylene (PTFE), modified PTFE, and copolymers of PTFE, offer a number of desirable properties, including excellent inertness and superior biocompatibility, and therefore make ideal candidate materials for artificial heart valves. Additionally, PTFE and expanded PTFE (ePTFE) have been used to create heart valve leaflets. It has been shown, however, that PTFE stiffens with repeated flexure, which can lead to unacceptable flow performance. Failure due to formation of holes and tears in the material has also been observed. A variety of polymeric materials has previously been employed as prosthetic heart valve leaflets. Failure of these polymeric leaflets due to stiffening and hole formation typically occurred within two years of implant. Efforts to improve leaflet durability by thickening the leaflets resulted in unacceptable hemodynamic performance of the valves, that is, the pressure drop across the open valve was too high. Conventional leaflets also experience wrinkling, which can be sites of potential failure of the heart valve.
Thus, there remains a need in the art for a biocompatible artificial heart valve, including leaflets, that is durable and reduces the occurrence of wrinkles during the cycling of the heart valve between open and closed configurations.